GFAP and Alzheimer disease: In this study, we investigated the changes over time in one of the most commonly used dMRI metrics for assessing diffusion rate in the cortex, namely mean diffusivity (MD), in a large cohort of individuals with either preclinical or prodromal AD stratified following the Aβ/tau (AT) framework.16 We evaluated associations between longitudinal changes in cortical MD and longitudinal changes in both CSF and plasma markers of astrocytic and microglial activity, such as GFAP, YKL-40 and soluble TREM2 (s-TREM2), in AD-biomarker-defined groups.